I'm doing the same thing and so I have read if you keep the chassis at the original length and you can replace out riggers as they replaceable parts, if you keep the axles, props, engine and gearbox this all adds up for the points system and entititals you to the Discovery or Range Rover registration which ever chassis you use.
I want to do the station wagon, and use it for a lot of towing as well for long distance travelling and use recycle waste cooking oil to cut the fuel cost down, but back to the towing I have read so many reports of rear crossmembers being bent out of shape while doing serious towing. I'm going to make my own re-enforced crossmember to make myself feel more comfortable while towing a flatbed trailer when loaded up. The rear crossmember are mostly 2mm I want to go to 5mm and use a length of boxed section to do this and still re-enforce the towing point, so may think this a bit over the top but that may be so but I won't be left replacing a bent back end in the future.
Has anyone fitted rear long range fuel tanks to a discovery hybrid and are they an easy fit???
ALAN
Sheffield S25